GB1568256A - Device for retaining a prosthetic elemnet on an osseous part - Google Patents

Description

PATENT SPECIFICATION

( 11) ( t 21) Application No 8029/77 ( 22) Filed 25 Feb 1977 ( 19) N ( 31) Convention Application No 7605 598 ( 32) Filed 27 Feb 1976 in = ( 33) France (FR)

= ( 44) Complete Specification published 29 May 1980

Ut ( 51) INT CL 3 A 61 F 1100 A 6 IC 8/00 M-1 ( 52) Index at acceptance A 5 R AP DJ ( 54) DEVICE FOR RETAINING A PROSTHETIC ELEMENT ON AN OSSEOUS PART ( 71) I, JEAN ANTOINE ERLICH DEGUEMP, a French citizen, of 20 Rue de Vintimille, 75009 Paris, France, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: -

The present invention concerns a device for ensuring the retention of a prosthetic element on an osseous part, more particularly the attachment of a dental prosthesis to a maxillary bone.

It is known that the fitting in position and retention of a prosthetic element and, moreover, a removable dental prosthesis, poses numerous problems related an one hand to the morphology and the physiology of the maxillary bones and on the other hand to the function of the said prosthesis.

Indeed, removable dental prostheses must be maintained in place satisfactorily to permit the wearer of the prosthesis to speak and chew food: moreover, they must be capable of being alternatively taken out and replaced to ensure their cleaning as well as the care of the mouth cavity.

The traditional mechanical cup fittings, springs or special projections, as well as sometimes causing painful pressure on the mucous membranes, are not very effective and are poorly tolerated.

Furthermore a well known disadvantage of these traditional prostheses is their poor retention, a disadvantage which becomes worse with time.

In an attempt to remedy this disadvantage, it has been proposed to fix prosthetic implants in the osseous foundation constituted by, for example, a maxillary bone Such a technique, however, necessitates the traversal of the mucous membrane and the retention in the latter of fixing elements, which risks the introduction of microbial infections and the irreparable destruction of the osseous foundation.

However, recently a solution has been proposed which affords numerous advantages and which consists in the retention of the prosthetic element by means of magnetic forces produced by magnetic systems disposed partly under the mucous membrane of the dental foundation and partly in the prosthetic element.

This technique has the advantage of not 55 creating any permanent lesion in the mucous membrane, simplifying the construction of the prosthesis and making them moreover more aesthetically attractive and less disagreeable for the wearer, as well as allow 60 ing improved retention compared with that obtained by traditional devices.

The present invention relates particularly to improvements applicable on one hand to the structure of the part of the magnetic 65 device which is associated with the maxillary bone and on the other hand to the means of insertion and retention of the said part of the magnetic device in the osseous part, which should be the most dense and the 70 least evolutive.

Indeed, one of the problems posed by the aforementioned technique prior to the invention lay in the anchoring of the magnetic device to the bone and in the necessity of 75 doing this in such a way it is keyed to the osseous part so as to avoid displacement of the magnetic element associated with the said part as a result of force exerted on the prosthetic element pressing the latter onto 80 the mucous membrane, which can give rise to distress to the wearer if not lesions of the mucous membrane, leading to rejection of the device Now this type of force exerted on the prosthetic element is fairly frequent 85 since one has to be able to remove the prosthetic element for the purpose of frequent cleaning.

According to the present invention there is provided a magnetic attachment device for 90 use in retaining a prosthetic element on an osseous part, such as a maxillary bone, the magnetic device being adapted to be housed in a cavity provided in the osseous part such that the cross section of the cavity at its 95 bottom is greater than the cross section at its entrance at the external surface of the osseous part, the said magnetic device comprising a foundation or seating structure having retaining means for locking it in the 100 1568256 2 1,568,256 2 cavity after its introduction into the latter, and at least one magnetic body, or a body capable of being magnetically attracted, attachable to the foundation or seating structure Once the magnetic device is fitted in place it cannot be displaced relative to the osseous part.

Moreover, although permanent fixing of the magnetic device may be effected after it has been put in place, whether by mechanical fixing of the magnetic body to the foundation or seating structure or by reconstitution of the bone itself around the magnetic body, it is envisaged, according to a preferred embodiment of the invention, that the magnetic body be connected to the foundation or seating structure before the housing of the device in the cavity.

Such a preferred arrangement permits, among other things, eventual replacement of the magnetic body without the necessity of again touching the bone.

The invention facilitates the insertion of the foundation or seating structure and avoids the development of localised stresses at the bone surface due to the attractive forces developed by the magnetic elements.

The method used for the insertion and fitting of the foundation or seating structure consists in the preparation of the cavity in the osseous part such that the cross section of the cavity at its bottom is greater than the entry cross section of the cavity at the external surface of the osseous part, the introduction of the foundation or seating structure into the cavity and the spreading out in the interior of the cavity of at least one part of the foundation or seating structure in such a way that at least one of the dimensions of the spread out structure is greater than at least one dimension of the entry section of the cavity, to achieve thereby the retention of the foundation or seating structure in the cavity.

The or each magnetic body may be retained in the foundation or seating structure by the attractive forces developed by the magnetic body itself, and/or mechanical retaining means with which the foundation or seating structure may be provided.

The foundation or seating structure may be formed with different shapes and particularly may be constituted by a bar or plate of magnetic material, preferably of soft iron, capable of assuming a retracted position permitting its introduction into the cavity of the bone and an extended position ensuring its locking engagement in the bone cavity, in this case, the magnetic body may be constituted by a permanent magnet which is retained by its own magnetic forces against the seating structure.

According to another embodiment, the foundation or seating structure may be formed by a casing having a seat or housing adapted to receive the said body The casing may be elastically deformable and may have a part of smaller cross section than the corresponding cross section of the said body, so that the introduction of the casing into the bone cavity and its extraction are possible as long as the said body has not been placed in position in the casing, the introduction of the body into the casing resulting in expansion by elastic deformation of said part thereof to anchor the casing in the bone cavity.

In an alternative embodiment the foundation or seating structure comprises a casing having two parts between which a spring is provided, the action of the spring tending to spread-out the casing, and each part of the casing having a projection permitting the locking of the casing in the bone cavity upon spreading-out of the casing Releasable means may be provided to keep the two parts forming the casing together in a retracted state, with the spring compressed.

It will be noted immediately that the casing once put in place in the cavity of the bone is adapted to remain therein permanently forming thus a key with the bone by means of scar tissue.

On the contrary, the magnetic body will preferably be removably fitted in the said 95 casing: upon the first surgical operation it is then possible to fit the casing in position in the cavity without the magnetic body, the latter being inserted in the casing afterwards In this way, the magnetic body is 100 spared almost all the operations, thereby avoiding the risk of damage or contamination of the magnetic body Moreover, thanks to this arrangement, it will be convenient eventually to withdraw 105 only the magnetic body for its replacement by another if the need for this arises.

There will now be described, by way of non-limiting example, some embodiments of the invention, with reference to the appended 110 drawings in which:

Figure 1 is a schematic sectional view of a prosthetic element fitted on the upper maxillary bone by means of a device according to the invention: 115 Figures 2 and 2 a show in front elevation the stages of incision and of lifting of the mucous membrane in order to expose the bone; Figure 3 is a section on an enlarged 120 scale showing a cavity profile formed in the bone; Figure 4 shows the formation of extensions in the cavity intended to serve for support of the seating structure to prevent 125 its extraction, Figure 4 a is a sectional view similar to Figure 2 showing the cavity formed in the bone; 1,568,256 1,568,256 Figure 4 b is a view according to the arrow I Vb of Figure 4 a; Figure 5 represents in perspective a first embodiment of a seating structure forming part of a device according to the invention; Figures 5 a and 5 b show schematically the fitting in place of the seating structure of Figure 5 in the cavity of the bone; Figure 5 c represents in perspective a second embodiment of a seating structure forming part of a device according to the invention; Figure 5 d shows the device of Figure 5 c placed in the cavity of the bone; Figures 5 e and 5 f represent a third embodiment of a device of the invention; Figures 5 g and Sh represent a fourth embodiment of a device of the invention; Figure 6 is a perspective view partly cut away of a casing of a magnetic device according to another embodiment intended to be inserted in the cavity of the bone; Figure 6 a is a view from below of the casing of Figure 6; Figure 7 is a perspective view of a magnetic body intended to be lodged in the casing of Figure 6; Figure 7 a shows the magnetic device in place in the bone cavity.

Figures 8 and 9 are sectional views showing the retractable projection of the casing of Figure 6 in two positions.

In Figure 1 there is represented, in a schematic manner, a partial frontal section of the upper maxillary bone 1, having its mucous membrane 2, on which is fitted a dental prosthesis comprising a base-plate 3 carrying artificial teeth 4.

44 The retention of the base-plate in position on the bone is effected by a magnetic device designated generally by 5, comprising a magnetic body such that a magnet 6 placed in a cavity 7 of the maxillary bone and an 46 opposed magnetic body 8 (which may perhaps be a magnet or a body susceptible of being magnetically attracted) which is fixed to the base-plate 3.

Naturally, it is understood that in the case of a complete palatine base-plate, for example, the prosthesis will be maintained by at least two magnetic devices 5 situated on both sides of the jaw.

The base-plate 3 will not be described in detail, nor will the magnetic body 8, which are considered as known.

The present invention relates to the structure of the magnetic device 6 placed in the maxillary bone and the description which follows concerns this point more particulary.

There will be first described, with reference to Figures 2, 2 a, 3, 4, 4 a and 4 b, the manner in which the cavity in the maxillary bone is 06 prepared in order to receive the magnetic device 6 As can be seen in Figure 2, after having incised at I the mucous membrane 2 at the locality where the cavity is to be formed, the mucous membrane parts 9 and are widely spread apart (Figure 2 a) to 70 expose a surface 11 of the maxillary bone sufficient for the formation of the desired cavity.

There is then made in the maxillary bone (Figure 3) a roughly rectangular cavity 12 75:

having a flat base 13 and vertical walls 14.

This rough cavity may be formed by a traditional milling head fitted to a drill, or by a chisel.

Upon completing the formation of the 80 rough cavity 12, extensions 17 of the cavity, at least in the two opposite walls 14 of the latter, are formed, as shown in Figure 4, by for example, a head 15 having an inverted cone bit 16 There is then obtained a slot 85 shaped cavity 12 having end extensions 17, as shown in Figures 4 a and 4 b.

The extensions 17 of the cavity 12 may have different shapes provided they form a base of the cavity 12 which is of greater 90.

width than the entrance of the cavity In the same way, it will be understood that the extensions 17 may be formed around the entire periphery of the base of the cavity 12 if necessary 95 The length L of the base of the cavity 12 measured to the extremes of the extensions 17 is greater than the length I measured across the mouth of the cavity (Figure 4).

Consequently, when the magnetic device is 100 placed in the interior of the cavity, as described later, good retention of the magnetic device is obtained.

Some embodiments of a magnetic device 6 intended to be inserted in the cavity of 105 the maxillary bone will now be described.

The magnetic attachment device is in two parts, that is to say on the one hand a seating structure which will be inserted in the cavity and destined to remain there per 110 manently, and on the other hand, a magnetic body or a magnetisable body which can be associated with the seating structure, either in a removable manner or in a nonremovable manner 115 Referring to Figure 5, there has been shown a seating structure of particularly simple form since it consists solely of a small bar of soft iron designated generally by 20 which is reduced in section in its 120 median part at least at 21 throuch its thickness and, if desired, also at 22 along its width in a manner permitting bending of the bar into the folded shape shown in full outline in Figure 5 the branches 23 and 125 24 situated on opposite sides of the reduced section forming a "V" It is understood th-at the wv'isted central portion permits spreading of the branches 23 and 24, permitting the restoration of the bar to the 130 1,568,256 rectilinear form represented in broken outline in Figure 5.

This bar 20 is such that when folded it can be introduced into the bone cavity 12.

Indeed the length 11 (see Figure 5 a) of the folded bar will be less than the length I of the cavity.

Once introduced into the cavity 12 in the manner represented in Figure 5 a it will suffice immediately to introduce the magnet (see Figure 5 b), exerting on the latter a vertical force in the direction of arrow F to cause the opening of the bar and its return to the rectilinear position in which the total length 12 is greater than the length I of the mouth of the cavity 12 In this way the bar becomes keyed in the cavity and cannot be withdrawn again.

Moreover, the maintenance in place of the magnet in the cavity is effected simply by contact with the bar 20 of soft iron.

This embodiment of a device according to the invention is however not preferred since there is a risk that the reconstitution of the bone will permanently trap the magnet in the cavity and prevent its eventual withdrawal should this be necessary.

This is why it is preferred, in the following embodiments, to provide a foundation or seating structure having a housing for the magnet which separates the latter from the bone and ensures perfect removability af the magnet In this respect the seating structure shown in Figures 5 c and 5 d constitute an interesting variant.

The seating structure comprises a casing indicated generally by 26 constituted by four walls 26 a and 26 b opposed in pairs, this casing being open at the top and bottom.

In two opposed walls, for example 26 b, of the casing 26, there are provided slots 27, and a small plate indicated generally by 28 of structure generally similar to the bar 20 of Figure 5 is inserted into the interior of the casing This plate 28 has a central part of reduced cross-section, for example, reduced thickness, 29 allowing it to adopt a first stable shape in the form of a "V", as seen in Figure 5 c, as a result of which the ends 30 of the plate 28 are engaged in the slots 27 without, however, projecting appreciably outside the casing.

Having inserted the casing 26 in place in the cavity 12 of Figure 5 d it sufficies to introduce the magnet 31 into the interior of the casing 26, exerting a vertical force on the reduced thickness part 29 of the plate 28 The latter is thereby extended, its arms being guided by the slots 27 so as to cause their projection beyond the exterior of the casing into the extensions 17 of the cavity 12 This position is indicated in broken outline in Figure 5 d and causes keving of the seating structure in the interior of the cavity.

56 If desired, the retention of the magnet 31 in the casing can be completed by mechanical means comprising in this example deformable tabs 311 (represented in broken outline in Figure 5 c) extending from at least two opposite walls of the casing, the tabs 70 311 being deformed to retain the magnet 31 once the latter has been engaged in the casing 26.

Figures 5 e and 5 f illustrate a third embodiment which utilises an annular casing 35 75 adapted to be inserted in place in a cavity which, in this example, is a circular cavity 14 a having a peripheral radially outward extension 17 a at its base.

Slots 35 ', for example four in number, 80 are formed in the casing 35 and are adapted to cooperate with a cruciform plate designated generally by 32 in Figure 5 e This plate has a central zone 34 from which there extend four arms 33 which together lie on 85 the surface of a conical section.

The material used for the fabrication of the plate 32 is at least partially malleable so as to allow the exertion of a force on the central zone 34 to cause squashing resulting 90 in extension of the arms 33 which then become engaged in the interior of the extension 17 a of the cavity 14 a The plate 32 for its part may advantageously be made of soft iron or, if desired, of plastics material 95 In the case where the plates 28 or 32 are made of plastics material, or in a more general manner, of a non-magnetic material, it will naturally be necessary to provide mechanical means for holding the magnet 100 in its casing, for example by the provision of tongues or ears of the type indicated in 311 in Figure Sc Naturally, in this case, the casings 26 and 35 could also be made of plastics material 105 In the embodiment of Figures 5 g and Sh, the foundation or seating structures comprises an elastically deformable casing formed by a simple ring of plastics material, generally indicated by 36, one part 37 of 110 which is cylindrical and the lower skirt 38 of which is of frust-conical form converging towards the axis of the ring 36 This skirt 38 is formed by a series of teeth 381 separated one from another by gaps 41, this 115 arrangement allowing expansion or contraction of the skirt 38 in a manner which is in itself well known.

It will be noted that each tooth 381 has at its base a heel 39 projecting towards the 120 outside and intended to ensure the hooking of the ring 36 in the bone cavity 12 as is more particularly shown in Figure 5 h.

Moreover, inside the ring 36 a shoulder is provided which is intended to keep in 125 place a magnet 42 introduced inside the ring.

In its undeformed condition, the ring 36 has an external diameter "D" which is smaller than the diameter of the mouth, of 130 1,568,256 5.

the bone cavity 12, so that it is possible to introduce the said ring into the cavity as many times as one wishes and to withdraw it without any kind of difficulty.

Moreover, the internal diameter of the ring 36 taken at the tips of the teeth 38 ' is smaller than the corresponding dimension of the magnet 42, so that once the ring 36 is placed in the cavity, it is sufficient to introduce the magnet into the ring and to exert on this magnet a vertical force F in order to effect expansion of the skirt 38 of the ring and engage the heels 39 in the extensions 17 of the bone cavity 12 At the end of the displacement of the magnet 42 the internal shoulder 40 of the ring 36 engages in a corresponding groove 43 provided in the periphery of the magnet 42, as shown in Figure 5 h.

In the embodiment of Figures 6 to 9, the casing 47 is substantially parallelepipedic, in this case, rectangular and is closed at one end by a flat bottom 48 The casing 47 has a front wall 49, a rear wall 50 and two lateral walls 51.

The bottom 48 has a fixed extension 52 projecting beyond the rear wall 50 and formed, for example, by a spring steel wire welded to the wall 50 at points 53 54, 55 and 56 It will be understood that the fixed extension 52 may alternatively comprise a blade which may be perforated to facilitate the formation of scar tissue.

The front wall 49 of the casing 47 has at the level of the bottom 48, a slot 57 formed for example, by a cut-out of part of the wall.

A displaceable extension of the casing 47 is formed, as can be seen particularly in Figures 6 a, by a spring steel wire 58 the ends of which are fixed on pivots 59 rotatably mounted in the bottom 48 of the casing This steel spring wire 58 is shaped so as to assume a tensioned retracted position inside the casing 47, in the form shown in Figure 6 a The wire 58 is kept in this retracted position by retaining means 60, formed, for example, by a hook pivotable about an axis 61 As soon as the hook 60 is opened, the tensioned steel wire 58 is released will move through the slot 57 to form a lateral extension projecting externally of the casing 47 and will assume the position shown in broken lines in Figure 6 a.

In this extended state, the tension in the spring wire 58 is relieved somewhat and its form is substantially similar to that of the fixed extension 52.

As a variation, the retaining means could be formed by a simple wire which is severed to release the wire 58.

The width a of the casing 47 (see Figure 6 a) is slightly smaller than at the opening of the bone cavity so as to permit the introduction of the casing into the cavity whereas the dimension A (with spread out extension wire 58) is substantially equal to the corresponding dimension L of the bottom of the bone cavity.

The walls 49 and 50 of the casing 47 70 have, moreover, elastically deformable means for ensuring the holding in place of a removable magnetic body 62 (see Figure 7) when the latter is placed in position in the casing after the said casing has been inserted 75 in the bone cavity.

These elastically deformable retaining means permit the introduction of the magnetic body and are formed, in the example shown, by male profiles comprising inwardly 80 projecting ridges 63 provided in the walls 49 and 50 of the casing 47, for example, by pressing However it will be understood that these retaining means could be formed by elastic tongues inserted within the walls 49 85 and 50 and fixed, for example, by welding or any other suitable manner.

The magnetic body 62 has at its base female profiles comprising locking grooves 64, intended to mate with the ridges 63 of 90 the casing 47 (see Figure 9).

With reference to Figure 7, it will be noted that in order to facilitate the holding of the magnetic body 62, particularly for its extraction from the casing, the upper face 95 of the magnetic body 62 may be provided with a cavity 65 traversed by a bridge piece 66 beneath which the tip of an extraction instrument may be inserted.

Claims (19)

WHAT I CLAIM IS: 100

1 A magnetic attachment device for use in retaining a prosthetic element on an osseous part, such as a maxillary bone, the magnetic device being adapted to be housed in a cavity provided in the osseous part such 105 that the cross section of the cavity at its bottom is greater than the cross section at its entrance at the external surface of the osseous part, the said magnetic device comprising a foundation or seating structure 110 having retaining means for locking it in the cavity after its introduction into the latter, and at least one magnetic body, or a body capable of being magnetically attracted, attachable to the foundation or seating struc 115 ture.

2 A device according to Claim 1, in which the foundation or seating structure is formed by a bar or plate having a retracted position permitting its introduction into the 120 bone cavity and an extended position permitting its locking engagement in the bone cavity.

3 A device according to Claim 2, in which the bar or plate is made of magnetic 125 material, for example, soft iron, and the said body comprises a permanent magnet which is retained against the bar or plate by the magnetic force developed by the said magnet 130 1,568,256 1,568,256

4 A device according to Claim 1, in which the foundation or seating structure is formed by a casing having a seat or housing adapted to receive the said body.

5 A device according to Claim 4, in which the means for locking the casing are formed by projections of the casing intended to abut against the bone in appropriate extensions of the bone cavity.

6 A device according to Claim 4, in which the casing is elastically deformable and has a part of smaller cross section than the corresponding cross section of the said body, so that the introduction of the casing into the bone cavity and its extraction are possible as long as the said body has not been placed in position in the casing, the introduction of the body into the casing resulting in expansion by elastic deformation of said part thereof to anchor the casing in the bone cavity.

7 A device according to Claim 6, in which the said part of the casing is formed by elastically deformable tongues.

8 A device according to Claim 5, in which at least one of the projections is displaceable between two positions, that is to say a first position in which, when the casing is placed in position in the bone cavity, the said projection is retracted and permits the introduction of the casing into the cavity, and a second position in which, after placing the casing in position in the cavity, the said projection is extended or spread-out in such a manner that the dimension of the casing measured at the level of the said projection is greater than that part of the cavity through which the casing has been introduced, thus ensuring the retention of the casing within the cavity.

9 A device according to Claim 8, in which the extension or spreading out of said projection is effected by elastic means against the action of which the said projection is retracted or withdrawn.

A device according to Claim 8 or Claim 9, in which at least one of the projections is formed of a deformable resilient wire fixed to the casing, the wire being under tension and retracted inside the casing in the said first position, and the wire projecting externally of the casing, the tension therein being relieved in the said second position.

11 A device according to the Claim 10, in which the resilient wire is fixed by at least one of its ends to one of the walls of the casing.

12 A device according to Claim 11, in which the casing has an opening through 60 which the resilient wire moves to pass from its retracted position to its projecting position.

13 A device according to Claim 12, in which the resilient wire is kept under tension 65 in the retracted position in the casing by retaining means which are releasable to free the wire.

14 A device according to any of the Claims 4, 5 6 or 9, in which the casing has 70 two parts between which a spring is provided, the action of the spring tending to spread-out the casing, and each part of the casing having a projection permitting the locking of the casing in the bone cavity 75 upon spreading-out of the casing.

A device according to Claim 14, in which the casing has releasable means to keep the two parts forming the casing together in a retracted state, with the spring 80 compressed.

16 A device according to Claim 5, in which the projections of the casing are formed by heels integral with the walls of the casing 85

17 A device according to any of Claims 4 to 16, in which the means for holding the said body in the casing are formed by at least one elastically deformable part of the casing, permitting the insertion and the ex 90 traction of the said body.

18 A device according to Claim 17, in which the elastically deformable parts of the casing are male profiles projecting into the casing and integral with the walls of the 95 latter.

19 A device according to Claim 18 in which the said body has female profiles cooperating to the male profiles of the casing and in which these latter become lodged 100 when the said body is placed in position.

A magnetic device for the retention of prosthetic elements substantially as herein described with reference to, and as shown in Figures 5 to 5 h, or Figures 6 to 9 of the 105 accompanying drawings.

M J STEPHENS & CO, Chartered Patent Agents, Royal Building, 11 St Andrew Cross, Plymouth PL 21 DS.

Agents for the Applicant.

Printed for Her Majesty's Stationery Office by Burgess & Son (Abingdon), Ltd -1980.

Published at The Patent Office, 25 Southampton Buildings, London, WC 2 A l AY from which copies may be obtained.